From the figure in Solution 6 above

$m = \dfrac{y}{x}$

$\dfrac{dm}{dt} = \dfrac{x \dfrac{dy}{dt} - y \dfrac{dx}{dt}}{x^2}$

where

x = 16 ft

y = 12 ft

dx/dt = 1.5 ft/sec

dy/dt = -2 ft/sec

$\dfrac{dm}{dt} = \dfrac{16(-2) - 12(1.5)}{16^2}$

$\dfrac{dm}{dt} = \dfrac{-50}{256}$

$\dfrac{dm}{dt} = -\dfrac{25}{128} \,\, \text{ per second } \,\, $

$\dfrac{dm}{dt} = \dfrac{25}{128} \, \text{ per second decreasing}$ *answer*